What Is Circadian Rhythm and How Can It Impact Mood?
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How Your Emotional Health Depends on Your Biological Clock

Light and dark are powerful conditions: each can send your body into or out of different states of consciousness, emotion and performance. As the earth cycles through a bright day and dark night in 24 hours, so too does your body. This is your circadian rhythm, and a lot depends on it.

You’ve probably felt the fatigue, weariness and irritability that come with a change to your sleep schedule, but the effects can run deeper than heavy eyelids and a short fuse. A disrupted circadian rhythm will likely impact your immediate mood, but it can interfere with your long-term emotional health, too.

About the Body’s Clocks and Rhythms

Most living things have circadian rhythms, the biological changes that happen within the body at various times in the day. But a circadian rhythm is more complex than it might seem, since it rests on so many smaller reactions, events and responses.

The Importance of Your Biological Clocks

Several smaller biological clocks determine how your circadian cycle proceeds. Molecules in different cells interact in groups throughout your body, and these are separate timers that trigger different events that keep your body’s systems working in tandem.

Together, and under the supervision of the master clock in your brain (a cluster of nerves on the hypothalamus), the clocks synchronize to produce your circadian rhythm.

Inside and Outside Factors Interact

Your circadian rhythm comes from within, but it’s influenced by your surroundings. Scientists have discovered genes that command circadian rhythms in a variety of animals and other organisms, but those genes are directed by several external factors, like:

  • Sunlight
  • Noise
  • Food
  • Stimulants (like caffeine)
  • Social interaction

How Your Body Reacts to the Rhythm

Your sleep cycle is the most obvious consequence of circadian rhythm, but an array of other natural processes are affected, too. Hormone release, body temperature, digestion, and other internal controls can benefit — or suffer — from the quality and regularity of your circadian rhythm.

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The Link Between Emotional Health and Circadian Rhythm

Major changes in the sleep cycle can disrupt the web of natural processes that keep your body rested, energized and balanced. A night or two of poor sleep likely won’t do much damage to your internal clocks, but drastic changes that come with shift work, jet lag, and season changes (especially in the extreme northern or southern regions) can interfere with your body’s balance.

The Importance of Melatonin

When daylight fades and bedtime approaches, your brain releases melatonin, a natural chemical that induces sleep.

So, when the number of daylight hours decrease, or you have to exert yourself at night, or the length of either phase changes, your melatonin production can falter. In turn, you will lose out on restful sleep, and your body and mind will suffer the consequences.

Poor Sleep Breeds Depression

Both a lack of sleep and a major change in your sleep patterns can alter your biological rhythms to troubling degrees. Over 80 percent of people with depression report sleep problems, and evidence suggests that the amount of deep sleep decreases right before the onset of depression.

Multiple shift changes, frequent episodes of jet lag, or other major sudden adjustments to your circadian rhythm can trigger your internal clock to induce REM sleep earlier.

What does this mean for you? Less deep sleep, which could set the stage for depression.

Rhythm Problems Can Lead to Other Mood Disorders

Although experts haven’t found out exactly how circadian rhythms influence emotional balance, there does seem to be a link between circadian rhythms and a range of emotional ailments, including unipolar mood disorders, bipolar moods disorders, and seasonal affective disorder (SAD).

In contrast to clinical depression, those suffering from SAD tend to sleep earlier, sleep more, and eat more during the shift to shorter, darker days.

Getting Your Circadian Rhythm Back on Track

If you’ve been suffering from frequent major time changes and you’re noticing your mood or outlook has declined, it’s time to focus on resetting your internal clock.

A test known as the dim light melatonin onset (DLMO) can determine how your circadian rhythm is functioning. A simple saliva sample can provide the evidence your doctor needs to make an assessment.

Adjusting circadian rhythms can be done in a couple of ways. Bright light and low-dose melatonin are good places to begin — they’re both readily available, and neither is associated with uncomfortable side effects.

In each case, the idea is to use energizing light or the natural sedative effect of melatonin to shift your rhythm back to normal. However, if the therapy isn’t timed correctly, you could actually shift in the wrong direction.

In addition to the DLMO test, you need to determine whether you’re an early bird or a night owl to know how to time your light exposure and melatonin intake.

Many people with SAD and major depressive disorders (MDD) have the phase-delayed type of circadian misalignment. For these sufferers, bright light in the morning and a dose of melatonin later in the day is often the way to go.